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 ::: Emulex Fibre Channel Switches  



Emulex is the computer industry's preeminent source for a broad range of advanced storage networking infrastructure solutions
 

Emulex technical briefs

Switching Basics with the InSpeed SOC 422

Technology Brief

Purpose

This technology brief explains how switching occurs in an arbitrated environment when using Emulex’s InSpeed technology as implemented in the InSpeed SOC 422. Emulex’s InSpeed technology provides economical acceleration of Fibre Channel connectivity for both the Entry Level SAN (ELS) and Embedded Storage Switch (ESS) markets.

Shared Bandwidth

In a Fibre Channel (FC) disk storage system based on the FC Arbitration (FC-AL) standard, up to 126 devices and one fabric connection may exist in a single physical address (AL_PA) space. Data within an AL_PA space physically travels from node to node in a daisy-chain fashion, ultimately traveling in a circuit, as shown in Figure 1. Control by a device on the system is obtained through the process of arbitration, after which the device winning arbitration sends or requests data. In single duplex mode, only one device is transferring data at any point in time. In full duplex mode, two devices may communicate with each other at the same time.

FC-AL is the protocol used in the back-end of most storage systems. FC-AL is mature and stable, but the downside is that all of the devices do share the same bandwidth under normal conditions. As devices are added to the storage system, performance is always affected since each device adds more latency. This means the time required traversing the shared bandwidth path increases, reducing overall performance. This is the reason most vendors limit the number of devices on a shared bandwidth or controller path to 40-64 devices.

Switched Bandwidth

Emulex’s InSpeed technology used in the InSpeed SOC 422 introduces switching to FC-AL topologies as shown in Figure 2. However, before explaining InSpeed switching, normal arbitration will be discussed.

Shared Arbitration Sequence

Using Figure 1 as the reference, when Initiator 1 (I1) wants to request data from Disk 3 (D3), I1 starts by requesting ownership of the channel by arbitrating. I1 sends an Arbitration (ARB) ordered set (I1,I1) to Initiator 2 (I2). I2 determines that it does not want ownership and passes the ARB on to Disk 2 (D2). D2 does not want ownership and passes the ARB on to Disk 4 (D4). This process continues until the ARB returns to I1. The process of getting its own ARB back completes channel ownership and I1 can then send an Open command (OPN) to D3 to start an actual data transfer sequence. Each additional device adds time, increasing latency and therefore negatively affecting performance.

Switched InSpeed Arbitration Sequence

Using Figure 2 as the reference, when I1 wants to request data from D3, I1 starts by requesting ownership of the channel by arbitrating and sending an ARB (I1,I1) to the InSpeed SOC 422. The InSpeed SOC 422 evaluates the arbitration request and, based on multiple criteria (such as the port type) may immediately return the ARB back to I1. I1 can then immediately send an OPN to the InSpeed SOC 422. This process substantially reduces latency in a FC-AL system, dramatically improving system performance.

InSpeed SOC 422 Switching

An OPN request sent by a device to the InSpeed SOC 422 is evaluated and the router dynamically forms a connection within the non-blocking crossbar switch core between the ports where the Source (SRC) and Destination (DST) devices are located. Subsequently, a conversation between the SRC and DST commences. This process is very similar to the point-to-point switching offered in fibre channel fabric switches. The dynamic crossbar switch used in the InSpeed SOC 422 is fundamentally identical to the crossbar switch used in fabric switches. This process makes the performance of fabric switches and InSpeed switches indistinguishable.

InSpeed Diagnostics

In addition to the improved system performance benefits made possible with the InSpeed SOC 422, system reliability is vastly improved. New levels of drive and drawer level fault isolation and diagnostics are made possible in an InSpeed SOC 422 environment. For example, the time required in performing drive reconstruction when a RAID drive fails is dramatically reduced. Even when a mirrored drive is replaced, the reconstruction time is reduced. The ability to conduct multiple, simultaneous conversations through the crossbar switch is a primary factor in this time saving.

Summary

The dynamic non-blocking crossbar switch core used in the InSpeed SOC 422 allows multiple conversations to occur at the same time. Using Figure 2 as an example, I1 can communicate with D4 at the same time that I2 communicates with D3. The latencies inherent to ordinary shared bandwidth topologies are stripped away and performance matches point-to-point fabric topologies.

Overall, the crossbar, non-blocking dynamic switching introduced with the InSpeed SOC 422 provides performance levels previously unattainable and allows full scaling to the FC-AL node count limit of 127 nodes while improving storage system performance. From a system level perspective, InSpeed is 100% FC-AL compliant, but performance is accelerated through the use of the crossbar switch. The total cost of ownership is also significantly reduced through the extensive diagnostics features available with InSpeed devices.

Contact 9 to 5 computer  to learn more about how InSpeed can increase the reliability, availability, serviceability and performance of your storage system designs.


 

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*Price and availabilities subject to change without any notice. Not responsible for typographical errors.


 

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